1. Technical Field
The present disclosure relates in general to methods for producing hydrocarbon gases from subterranean reservoirs, and more particularly to methods of preventing or lessening deposition of elemental sulfur in production tubing, valves, and other equipment during production of “sour” or “acid-gas” containing hydrocarbon fluids.
2. Background Art
Deposition of elemental sulfur in piping and other equipment during production of sour hydrocarbon gases from subterranean reservoirs is a well-known problem. Elemental sulfur is precipitated from the gas phase with the drop in pressure and temperature as the gas flow up the production tubing. Sulfur freezes at 117° C. (243° F.) into a solid/semi-solid that sticks to the tubing, plugging the tubing, which in turn affects and/or stops continual gas production.
In general, the solution in the past has been to inject various organic or inorganic solvents or solvent-containing fluids to dissolve the sulfur in the tubing (and in some cases dissolve sulfur in the reservoir), and remove the solid sulfur deposits. One such organic solvent is dimethyl disulfide (DMDS). Other dialkyl disulfides have been used. Solvents such as DMDS are very toxic chemicals with horrible odor and which therefore present health, safety, security, and environmental issues. Disposal of the toxic product is also very specific with a limited number of treatment centers which are able to manage the toxic products. The disposal is expensive and can be challenging to implement. The cost of solvent washes drastically increases operating costs, to the point that high production rate wells can actually become uneconomical to produce, leaving a large potential reserve of gas in the reservoir.
Another solution to the problem is to chemically react elemental sulfur with an aqueous solution capable of chemically reacting with sulfur to form a water-soluble sulfur derivative. However, as the elemental sulfur is oil-wetted and non-polar, these compositions have typically included an effective amount of a wetting agent or surfactant. U.S. Pat. No. 3,909,422 discloses use of solution of about 3 to about 50 percent (w/w) of an inorganic material reactive with sulfur selected from the group consisting of alkalies, sodium sulfite and sodium bisulfite and about 10 ppm nonionic surfactant wetting agent, or an aqueous solution of about 3 percent (w/w) to about 50 percent (w/w) sodium hydroxide and about 10 ppm to about 100 ppm of an ethylene oxide adduct of nonyl phenol.
Other United States patents include U.S. Pat. Nos. 4,290,900; 4,248,717; 4,239,630; 4,230,184; 5,585,334; 4,728,447; 5,028,343; 5,104,557; 4,543,193; 3,913,678; 4,248,717; 4,295,979; 4,633,949; 4,710,305; 4,773,480; 4,773,483; 4,839,154; 4,888,121; 4,949,790; 4,978,512; 3,909,422; 3,393,733; 3,531,160; 3,545,916; 3,744,565; 3,846,311; 4,988,389; 5,126,059; 5,188,179; H1,147; 5,705,135; 6,622,790; 6,832,653; 7,037,434; 7,978,005; 7,093,663; and 7,198,106.
There is a continuing, pressing need from the HSSE and economic standpoints to reduce the amount of chemical used in producing hydrocarbons. The methods of the present disclosure are directed to these pressing needs.